Fine structure of leydig and sertoli cells in the testis of immature and mature spotted ray Torpedo marmorata

Abstract

An ultrastructural investigation revealed the presence of true Leydig cells in the testis of sexually mature specimens of Torpedo marmorata. They showed the typical organization of steroid-hormone-producing cells, which, however, changed as spermatocysts approached maturity. In fact, they appeared as active cells among spermatocysts engaged in spermatogenesis, while in regions where spermiation occurred, they progressively regressed resuming the fibroblastic organization typically present in the testis of immature specimens. Such observations strongly suggest that these cells might be engaged in steroidogenesis and actively control spermatogenesis. Sertoli cells, too, appeared to play a role in spermatogenesis control, since, like Leydig cells, they showed the typical aspect of steroidogenic cells. In addition, the presence of gap junctions between Sertoli cells suggests that their activity might be coordinated. After sperm release, most Sertoli cells were modified and, finally, degenerated, but few of them changed into round cells (cytoplasts) or round cell remnants, which continued their steroidogenic activity within the spermatocyst and the genital duct lumen. From the present observations, it can be reasonably concluded that, in T. marmorata, spermatogenesis depends on both Leydig and Sertoli cells, and, as postulated by Callard (1991), in cartilaginous fish, the function of the Leydig cells as producers of steroids might be more recent and subsequent to that of Sertoli cells. In this regard, it is noteworthy that, in immature males, when Leydig cells showed a fibroblastic organization, Sertoli cells already displayed the typical organization of a steroidogenic cell.

Cell junctions in fish seminiferous epithelium

“…Cadherins were also immunodetected in the basal region of SC in the cartilaginous fish T. marmorata (Prisco et al 2007), where ectoplasmic specializations had already been described (Marina et al 2002). These data indicate that the cadherincatenin system may be involved in the composition of SC-SC actin-related junctions in fish, just as they occur in other epithelia (Herrenknecht et al 1991;Ozawa and Kemler 1992).…”

“…However, despite being associated with sub-surface cisternae of endoplasmic reticulum, those junctions between adjacent SC present in S. canicula, unlike mammalian inter-SC junctions, lacked the subplasmalemal layer of filaments (Pudney 1995). Ectoplasmic specializations in cartilaginous fish homologous to those of mammals have been described in other cartilaginous fishes, such as Squalus acanthias and Torpedo marmorata testes, and these junctions were found to be composed of surface specializations between SC, a subplasmalemal layer of filamentous material and cisternae of the endoplasmic reticulum (Pudney 1995;Marina et al 2002).…”

“…In fish testes, SC-SC gap junctions had never been described until 1995 (Loir et al 1995), and they were first detected between the SC of the cartilaginous fish T. marmorata (Marina et al 2002). More recently, the gap junction protein connexin was first detected in fish testis of the catfish P. fasciatum, at the borders of spermatogenic cysts and in the SC cortical cytoplasm (Fig.…”

“…According to these authors, testicular connexin 43 mRNA levels in the brook trout, Salvelinus fontinalis, were significantly increased, and spermatogenesis was advanced in individuals after exposure to wastewater effluent. On the other hand, the functionality of SC gap junctions has never been demonstrated, and it remains unknown if these gap junctions reported in fish (Marina et al 2002;Batlouni et al 2005;de Montgolfier et al 2007) are capable of allowing the sharing of substances among these cells. Therefore, it would be very interesting to develop dye-coupling experiments to test the functionality of these junctions between SC.…”

“…While many studies have focused on topographical and functional interactions between the diverse cell types of the mammalian seminiferous epithelium, only a few studies have devoted particular attention to these aspects in fish. In this respect, the majority of available knowledge on fish refers to the morphofunctional characteristics of adhesive (Sprando and Russell 1987;Loir et al 1995;Pfeiffer and Vogl 2002), gap (Loir et al 1995;Marina et al 2002;Batlouni et al 2005) and tight (Abraham et al 1980;Silva and Godinho 1989;McClusky 2006) junctions. However, more recent investigations have started to reveal the molecular composition of these junctions (Batlouni et al 2005;Prisco et al 2007), their turnover during the reproductive cycle (de Montgolfier et al 2007) and that they represent a specific target for environmental toxicants, such as cadmium (McClusky 2006), or compounds present in wastewater effluents (de Montgolfier et al 2008).…”